1. Field of the Invention
The present invention relates to email, particulary, to a blocking method and a blocking apparatus for junk email.
2. Description of the Related Arts
Nowadays, the Internet has become popular, and a large amount of information is exchanged over the Internet. The information exchange includes conventional information exchange using email in addition to information publication on home pages. Today, however, an email address of an individual is leaked to an unexpected person, and many unsolicited email messages can reach the address. Conventionally, email software must be used as a measure to block harmful advertising or junk email, which is referred to as spam. With such a spam blocking method, it is possible to detect character strings which frequently appear in spam messages, or to filter email sent from particular email addresses. However, U.S. Pat. No. 5,619,648 providing such a method is not a complete solution, and spam transmission tricks become complex more and more, which leads to a vicious spiral.
Additionally, email that is desired to be received can possibly be deleted if it is mistakenly identified as spam and cannot be read, although such a case is rare. Namely, email messages including the same character string can be, for example, both sides about an issue expressed by that character string. Therefore, limitations naturally exist in the determination of whether or not received email is desired mail according to the detection of a character string.
Furthermore, since opportunities to notify others of an email address are increasing, it is almost impossible to determine from where an email address is known to a spammer. That is, today, individuals frequently set up home pages, and make information public. To clarify where the responsibility for the information carried on a home page rests, the mail address of the person who sets up the home page with the information is made public. In such a case, whoever views the mail address is not known on a worldwide scale, and the possibility that junk mail is transmitted from an unknown person has been increasing.
Since the method for processing email is already known, its detailed explanation is omitted in the following description. For the details of the method for processing email, please see, by way of example, “Sendmail (Nutshell Handbook)” written by Brayan Costales & Eric Allman, published by O'Reilly & Associates, Inc., 1997, or RFC (Request For Comments) distributed by the Network Information Center (NIC).
Also in a conventional system, it is possible to change the email address of an individual when the address is proved to be a spam target. However, in the conventional system, a single address is assigned to a single person, and also a charge is fixed per address in many cases. Therefore, it is difficult to change a contract with an Internet service provider, a normally used email address, or an address notified to other persons, each time spam harm occurs. This is, therefore, not a practical method.
Furthermore, since the cost on an email transmitting side is low, a huge pieces of email can be sent if only email addresses are known. Therefore, it is easy to simultaneously transmit a spam message to email addresses collected by some means or another from somewhere. Spam is a serious problem not only in countries, such as the U.S., where the popularity of the Internet is high, etc., but also in Japan.